Rig not moving mesh correctly
Blender uses solid bones with a head an tail separated by a body.  What you have here is many very small bones placed at the joint locations.  I am not very familiar with Maya but I think this is done in a Maya style where joints are king.  Basically when you are rotating a "joint" in your blend you are spinning a very small bone around a central axis.  You need the head of the shin bone for instance to be in the knee and the tail of the shin bone to be in the ankle.  Then when you select the bone in pose mode put the 3d cursor on its origin and make rotation pivot the 3d cursor.  When you rotate now you will see a stick bone rotating at the knee (like a real shin bone) and the mesh will move like you expect.  You may need to re-weight it but with doing one bone fast it seemed like it would be ok if I got everything straightened out.